1. Field of the Invention
The present invention relates to a process of forming a nitride semiconductor device type of high electron mobility transistor (HEMT).
2. Background Arts
A semiconductor device using nitride semiconductor materials have been practically popular in a field because of superior breakdown voltages inherently attributed to the nitride semiconductor materials. A semiconductor device type of HEMT is widely used in the field. Recht; F et al., has reported in IEEE Electron Device Letters, vol. 27 (2006) pages 205 to 207, that a HEMT has n+ regions beneath a source electrode and a drain electrode in order to improve contact resistance of those electrodes.
The n+ regions may be formed by implanting ions therein and subsequent annealing at a temperature higher than 1000° C. in order to activate implanted ions. However, such annealing sometimes degrades the quality of the mother semiconductor materials to be annealed. An insulating film made of inorganic material, conventionally a silicon nitride (SiN) film formed by a plasma enhance chemical vapor deposition (p-CVD) technique, may prevent the degradation of the semiconductor surface. However, after annealing and removing the insulating film, a surface of the semiconductor materials sometimes shows degraded morphology. A HEMT based on such a degraded surface shows an increased leak current and a lesser reliability.